Present-day automobile series lacquer finishes mostly consist of a clear coat/base coat finish that is applied to an electrophoretically primed and filler-coated bodywork. In the course of this, base coat and clear coat are preferably applied wet-on-wet, i.e. the base coat, after a flashing-off period, and optionally with heating and after subsequent application of a clear coat, is stoved together with the latter, as described e.g. in EP-A-0 038 127 and EP-A-0 402 772. Clear coatings suitable in this connection are described e.g. in EP-A-0 038 127 and EP-A-0 184 761.
In the case of the use both of one-component (1K) and of two-component (2K) clear coats, the lacquering operation is associated with emissions of environmentally harmful solvents. In the context of increasing efforts to protect the environment, the lacquer industry and the lacquer user take trouble that solvent emissions are largely avoided. A possibility is the use of 2-component systems. In the case for example of isocyanate-crosslinking 2-component clear coats, e.g. according to DE-OS 33 22 037 or DE-PS 36 00 425, overspray recycling is naturally not possible. As a result, that yields an increased amount of waste.
A further way of achieving this objective is the use of one-component highly solids-rich stoving clear coats in the production of multicoat lacquer finishes. However, the solvent content of such lacquer systems is generally at least 50 wt %. U.S. Pat. No. 4,419,407 even describes clear coats with a resin solids content of up to 65 wt % that can be used, applied wet-on-wet to flashed-off base coats, for the production of a multicoat lacquer finish. Those lacquers have the drawback that their application-technology properties as well as the surface of the finished coating are less advantageous than for lacquers with lower solids content.
DE-OS 22 53 300 describes hot-sprayable, solvent-free or low-solvent lacquer systems based on high-molecular polyesters with molecular weights of 1500 to 5000, low-molecular polyols and melamine resins. Alkyd resins in particular are described as polyesters. The examples still contain proportions of solvent of more than 20 % in the coating agents. These serve to reduce the viscosity.
DE-PS 26 29 930 describes hot-sprayable stoving coating agents, solvent-free or containing only low proportions of solvent, that are based on linear polyester resins with acid numbers below 15, preferably below 5 mg KOH/g, and methoxymelamine resin as crosslinker. The polyester resins contain aromatic structural units.
Pigmented coating agents are described both in DE-PS 22 53 300 and in DE-PS 26 29 930. Also these products are not sufficiently stable towards ultraviolet radiation.